Firefox triggers "server is offline" modal on form submission

[Myles Metzler]

Minor issue as forms are only used for setup and the message only flashes up while the server is processing the form.

[Myles Metzler]

issue is caused by existing ajax requests being canceled while the page is unloading this is detected as a timeout error; solution is to use beforeunload event to disable popup when reloading page or changing page.